[Amps] Miller-Larson effect on thoriated tungsten filaments / neat electronic soft-start

[Leigh Turner]

Hi Chris,

 

See the ON Semiconductor TDA1085C Data Sheet / App Note...all the needed
info' is succinctly contained there.

 

Leigh

 

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Chris Wilson
Sent: Tuesday, 25 June 2013 6:55 PM
To: amps at contesting.com
Subject: Re: [Amps] Miller-Larson effect on thoriated tungsten filaments
/neat electronic soft-start

 

 

> Yes those GE CL-60 NTC inrush limiting thermistors are helpful albeit 

> still yield a fairly fast rise time constant in the filament voltage.  The

> far gentler slow 3 to 4 second ramp up from the Triac controller is more

> elegant. The slow soft-start circuit is based on the ON Semiconductor

> TDA1085C IC chip and a 40A Triac.

> 

> In fact I've also got a couple of CL-60 thermistors (one in each leg) the

> primary of the Kenwood TL922 amp's filament transformer to trim /
fine-tune

> the steady-state filament voltage measured right at the tube socket to
circa

> 4.9 Volts, as the factory stock filament voltage is on the high side;
around

> 5.2 to 5.3 Volts. That slight over voltage can also shorten the 3-500Z
tube

> emission life.

> 

> Leigh

 

 

25/06/2013 10:24

 

Do you a schematic you would share for the Triac soft start setup

please Leigh?

 

Thanks.

 

-- 

       Best Regards,

                   Chris Wilson.

 

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